Grammar: What is a Comma Splice? (CS)

a comma splice (writing error)

A comma splice happens when a comma is incorrectly used between two independent clauses. For example:

It was Roy's birthday, he wanted to do something special.

The first clause, It was Roy's birthday, is called an independent clause [IC] because it represents a complete thought. This means you do not need anymore information to understand the sentence; it is complete.

The second clause, he wanted to do something special, is also an independent clause [IC]. It is a complete thought.

Rule: You cannot join two independent clauses [IC] + [IC] with a comma. If you do this, you create a run-on sentence, which is a common writing mistake.

How to Fix a Comma Splice

1. Use a period.

It was Roy's birthday. He wanted to do something special. (Correct)

2. Join the two independent clauses with a coordinating conjunction. Coordinating conjunctions, also called FANBOYS, are these seven words: for, and, nor, but, or, yet, so (you can remember them with the acronym F.A.N.B.O.Y.S.).

It was Roy's birthday, so he wanted to do something special. (Correct)

It was Roy's birthday, and he wanted to do something special. (Correct)

3. Use a semi-colon. Semi-colons can join two independent clauses. The sentences should be closely related (e.g. about the same topic).

It was Roy's birthday; he wanted to do something special. (Correct)

Adding a period is the easiest way to avoid comma splices. Remember that longer sentences are not necessarily better sentences.

To learn how to avoid creating comma splices, you need to learn the differences between independent and dependent clauses.

Independent Clauses (Main Clauses) vs. Dependent Clauses (Subordinate Clauses)

An independent clause is a complete thought. It presents a full idea. On the other hand, a subordinate clause is incomplete; you need more information to understand what the speaker/writer wants to say. Compare these clauses:

  • I love you (= independent clause; this is a full sentence. We can completely understand.)
  • If I love you  (= dependent clause; you need more information to make this a full sentence.)
  • The company hired several new workers (= independent clause. This thought is complete.)
  • Because the company hired several new workers (= dependent clause; you need more information to make this a sentence...(Because what?))
  • The Nile is a River. (= independent Clause)
  • which is in Africa (= dependent clause; this thought is not complete)

Note: When you try to write a sentence with only a dependent clause, you create a fragment. For example, "Because I was hungry." This is not a full sentence; it is only half a sentence. Fragments are another common grammar error.

Exercise 1: Identify the Type of Clause

Are the below clauses independent clauses (IC) which represent a complete though, or are they dependent clauses (DC) because they are incomplete?

1. I have never been to EgyptAnswer

IC. This is an independent clause. It represents a complete thought.

2. Although I have never been thereAnswer

DC. This is an dependent clause. 'Although' is a subordinate conjunction that begins a dependent/subordinate clause. This DC needs to be connected to an IC. Otherwise, it is not a sentence.

3. While I was watching TV in the living room yesterday nightAnswer

DC again. 'While' is a subordinate conjunction. It is only half a sentence (it is not complete).

4. Yesterday I found twenty dollars on the sidewalkAnswer

IC. This is an independent clause. It represents a complete thought.

5. In order to get good grades and become successfulAnswer

DC. This is an dependent clause. In order to what? The sentence is incomplete.

6. Since he had no moneyAnswer

DC. This is sentence is incomplete.

7. Greece has a population of roughly 10 million peopleAnswer

IC. It represents a complete thought.


To avoid comma splices, remember these rules of English grammar:

1. You cannot put a comma between two independent clauses [IC]

Canada is big, Russia is bigger. (Comma Splice)

IC , IC. (Incorrect)

2. You CAN put a comma between a dependent clause [DC] and an independent clause [IC]. (This type of sentence is called a Complex Sentence.)

Although Canada is big, Russia is bigger. (Correct)

DC, IC. (Correct)

You can also reverse the order to [IC] [DC]. (In this case no comma is required.)

Canada is big although Russia is bigger. (Correct)

IC DC. (Correct - no commas)

3. Conjunctive adverbs (words like "Therefore/However/As a result/For example/On the other hand") cannot join sentences. This means that you cannot put a comma before them to join two clauses. For example,

I was hungry, therefore, I went to the store. [Incorrect]

I was hungry. Therefore, I went to the store. [Correct = IC. IC.]

It was raining, however we went outside. [Incorrect]

It was raining. However, we went outside. [Correct = IC. IC]

Conjunctive adverbs are not conjunctions (they are adverbs like the words 'often', 'now', 'quickly'), so they cannot join sentences. Read the rules here.

Summary: Comma Splices

If you have two independent clauses ("He likes it" + "She likes it"), then you cannot join them with a comma. You can join them by adding a Coordinating Conjunction (FANBOYS), a Subordinating Conjunction (a word like 'if/because/even though' that begins a dependent clause), or a semi-colon. Otherwise, just put a period between the clauses.

Exercise 2: Identify the Comma Splice

1. Because the product arrived late, I was angry. Answer

DC, IC = Correct, not a comma splice..

2. The product arrived late, I was angry. Answer

IC, IC = Incorrect. This is a comma splice.

3. Yesterday, I ate soup, today I ate a salad. Answer

IC, IC = Incorrect. This is a comma splice. The words Yesterday and today are adverbs. They cannot join sentences.

4. Yesterday I ate soup, however today I ate salad. Answer

IC, IC = Incorrect. This is a comma splice. The word however is an adverb. It cannot join clauses.

5. The phone rang, so we answered it. Answer

IC,{FANBOYS} IC = Correct. You can join two independent sentences with a coordinating conjunction {FANBOYS} such as 'so'. This makes a Compound sentence.

6. The phone rang, then we answered it. Answer

IC,IC = Comma Splice. The word 'then' is not a conjunction. It is an adverb. It cannot join clauses.

7. Because the phone rang, we answered it. Answer

DC,{FANBOYS} IC = Correct. This is a Complex sentence.


As you can see, understanding which words are conjunctions is important to know how to use a comma. This is why even native English speakers often make this writing mistake. Avoiding comma splices takes time and study. I hope this lesson has helped.

How can you improve your English? The best way is to practice speaking and writing with a teacher who can give you immediate feedback. If you don't have a teacher, there is also free software such as Grammarly that can give you grammar feedback while you type.

If you have any questions, please leave them in the comments section below.

- Matthew Barton / Creator of (copyright)

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6 comments on “Grammar: What is a Comma Splice? (CS)

  1. Muhammad Mozammel Hossain (Posted on 8-4-2020 at 04:57) Reply

    It is very helpful posts.

  2. Laura (Posted on 8-6-2020 at 16:07) Reply

    Thank you so much Matthew. It is a very clear and useful page.
    I have a question, why is “Russia is bigger” an independent clause? In my understanding “bigger” is a comparative adjective, so I need another thing to compare with. It is because of that I think “Russia is bigger” is not a complete thought. Could you help me to understand this, please?


    1. mb Post author (Posted on 8-6-2020 at 23:54) Reply

      Hello. What you say is true, but still, the sentence “Russia is bigger” is grammatically complete, which makes it an independent clause. The sentence has a subject, verb, and complement. It doesn’t matter that we don’t know what it is bigger than (this is information can come from outside the sentence). Nothing _inside_ the sentence is missing. Here’s another example: “It costs five dollars.” <-- Is this a complete thought? Well, we don't know what "It" refers to, but still, the sentence is complete because there is a Subject and a Verb, and an object, which means there is nothing missing from the sentence. Now, if you compare this to "Although it costs five dollars" <-- this is an incomplete thought because the word 'although' suggests contrast with another idea _in the sentence_. This idea is missing, however. I hope this helps. It can be a bit confusing I admit.

  3. Laura (Posted on 8-7-2020 at 01:32) Reply

    OH! I got It! Thank you so much. I really appreciate your time and explanation with clear examples. I am learninga lot from you.

  4. Lizette Hernandez (Posted on 8-7-2020 at 02:22) Reply

    Hello Professor,

    I found this material quite helpful as the examples and exercises clarified my understanding of the topic.

    Your hard work and support in and out of the class are much appreciated!

  5. Andres C. Hernandez (Posted on 5-8-2022 at 08:14) Reply

    this post is awesome. Thanks for this explanation and all the examples

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